Abstract: A hard disk drive having a plurality of disks mounted on the rotor of a current limited, electronically commutated dc motor. Windings on the stator of the motor are divided into serially connected run and start sections and first and seconds drive circuits are provided to operate the motor by alternatively enabling the first drive circuit to pass currents serially through the two sections of the winding and enabling the second drive circuit to pass currents through only the run sections of the windings. During spin up of the disk drive to operating speed, the first drive circuit is enabled and the second drive circuit is disabled to drive the disks to the speed at which the back emf limits on the acceleration of the motor using both sections of the windings reduces the acceleration to the maximum acceleration achievable at the current limit using the run sections alone. Spin up is then completed by enabling the second drive circuit and disabling the first drive circuit.

Abstract: A method for optimizing settle characteristics of a read/write head on a data track on a rotating disk of a hard disk drive following a seek to the data track wherein each data track is assigned to a selected on of a plurality of concentric zones defined on the surface of the disk. Seeks are performed by a servo system in relation to a compensated velocity demand profile that provides velocities the head is to have at selected distances from a destination track and is selected for each zone by adding a velocity increment specific to the zone to a stored velocity demand profile for movement of the head in one direction and subtracted from the stored velocity demand profile for movement in the opposite direction.

Abstract: A hydraulic pump having a pump body formed by stacked plates mounted end-to-end. First and second ports for delivery and return of hydraulic fluid are formed through a port plate that is surmounted by a valve plate through which first and second main valve passages, each aligned with the first and second ports respectively, are formed. The valve plate is surmounted by a manifold plate in which first and second fluid distribution chambers, fluidly communicated with the first and second main valve passages respectively, are formed. A pump plate atop the manifold plate contains a gear assembly in a pumping chamber formed in the ends of the pump and manifold plates that draws fluid from one fluid distribution chamber and discharges it to the other.

Abstract: A method for effecting a transition from data track following by one data head adjacent one disk of a rotating disk data storage device to data track following by a second data head adjacent a second disk wherein the data tracks are part of a cylinder of tracks including a servo track followed by a servo head with an offset appropriate to each data track. A servo control circuit between the servo head and the coil of an actuator on which the heads are mounted receives a position error signal from the servo head and an offset signal from a microcomputer during following of each track and the transition is effected by adjusting the offset signal in a succession of discrete steps from the offset appropriate for one data head to the offset appropriate to the other data. Steps of the succession can have magnitudes equal to successively selected proportions of the offset signal difference for the two data heads or can vary alternatively between the offset signal difference for the two heads and a zero magnitude.

Abstract: A method of writing servo patterns to the surface of a disc of a hard disc drive without magnetizing the transducer head by means of which the patterns are written. The surface is initially magnetized in one direction through the transducer head while the disc is rotating to move the disc surface by the transducer head. Each servo pattern is subsequently written by passing a current through the transducer in the opposite direction for selected time interval. Following writing of each pattern, a current is passed through the transducer head in the direction used to initially magnetize the disc for a time interval equal to the time interval during which the pattern was written.

Abstract: A prewrite compensation circuit for selectively delaying the writing of non-zero bits of data streams to disks of a hard disk drive. The hard disk drive includes a write circuit for writing the non-zero bits to selected portions of selected disk surfaces and selected write delays are effected by a variable delay circuit that receives the data stream from a shift register through which the data stream is passed. The amount of delay is determined by a delay word entered into a latch connected between the variable delay circuit and a RAM in which delay words are stored at addresses selected for each delay word in relation to the pattern of bits of the data stream surrounding each non-zero bit, the disk surface to which each data stream is to be written and the portion of the surface to receive the data stream.

Abstract: A method for maximizing throughput of a hard disk drive by adaptively seeking to a data track at which data is to be stored and adaptively commencing the reading or writing of data in accordance with the movement of the read/write head in the proximity of the data track. In each seek to a data track, an approach time for movement of the read/write head from the entry into a fine control region about the track to a selected distance from the track is measured and reading or writing is commenced at the end of a delay time selected in relation to the approach time. The tracks on the disk are assigned to a plurality of concentric zones to which profile adjustment bins are assigned to contain an adaptive profile adjustment that is added to terminal portions of a read/write head velocity demand profile in accordance with which seeks to tracks are effected.

Abstract: Apparatus for supporting transducer heads of a hard disk drive wherein the heads are mounted on transducer support arms that are, in turn, mounted on extensive fingers formed on an actuator that moves the heads across surfaces of data storage disks. Two holes are formed through each finger to form two coaxial sets of holes on the actuator body and one hole in each finger receives a tubular boss formed about one of two equally spaced holes formed through one end of each support arm each arm. Bosses inserted into coaxial holes in the fingers extend thereinto from the same direction and are swaged to fix the support arms to the actuator by passing a ball through the bosses from the opposite direction. The support arms are constructed by spot welding swage plates, each having two holes formed therethrough and having a boss about one hole, to leaf members, similarly having two holes formed therethrough, whereon the transducer heads are mounted.

Abstract: A method for eliminating overshoot of a destination track by a servo head of a rotating disk data storage device during seeks wherein the seek is carried out in accordance with an adaptive velocity demand profile selected to undershoot the destination track by an amount sufficient to offset overshoot arising from an incapacity of the servo head to follow a velocity demand profile. Prior to performing the seek, the servo head is moved a distance about a null position on the disk at which the only force on the actuator on which the head is mounted arises from a constant current passed through the actuator and the time for the movement is measured and utilized to select the adaptive demand profile. Adaptive demand profiles are obtained by performing seeks while modifying a nominal profile to eliminate actuator current ringing at the end of the seek.

Abstract: Servo disk, including three types of servo patterns distinguishable by phase, are stored in concentric tracks on a magnetic information storage disk. For phase recognition, the pattern types are arranged in triplets of sectors, each sector having a radially extending plurality of only one type of pattern with consecutive patterns in a sector being separated by three track spacings. The patterns are further arranged in radially repeating frames, each including one of each type of pattern, and the patterns are radially offset within a frame by one track spacing from one type of pattern to the next. The patterns have a radial width greater than a track spacing and, in one embodiment, are divided radially into two portions spaced apart by a distance less than one track spacing.

Abstract: A method for assigning tracks on a magnetic data storage disk to different zones in which data is written at selected zone frequencies so as to write data on the tracks at the maximum frequency that will limit the read/write error rate to a preselected value. A plurality of data bit groups is written onto selected tracks and read while checking for error to determine an error indication parameter for each of the zone frequencies. Tracks are assigned to frequency zones by determining such parameter for all tracks and assigning each track to the zone corresponding to the maximum frequency for which the error indication parameter is below the preselected value or by determining circular paths at which the error indication parameter has the preselected value for each of the selected frequencies and assigning all tracks between two consecutive circular paths to the lower of the two frequencies defining the circular paths.

Abstract: An apparatus for providing sector location pulses to a controller of a rotating disk data storage device having a counter clocked in proportion to the disk rotation rate and an accumulator for accumulating times to sectors on the disk. A comparator connected to the counter and the accumulator enables an accumulator clock for repetitive clocking of the accumulator at such times the contents of the accumulator do not exceed the contents of the counter. A sector location pulse generator connected to the comparator generates the controller pulses, when enabled, concurrently with the accumulator clock signals. A master reset generator resets the first counter and the accumulator each time an index location on the disk passes a transducer head used to read and write data to and from the disk and a partial reset generator resets the accumulator each time the transducer head is moved between tracks on the disk.

Abstract: An adaptive prewrite compensation apparatus for writing data flux transition data on a magnetic medium, the apparatus incorporated in a disk drive assembly. A serial data pattern is introduced into the apparatus from a drive interface in digital form and is encoded. A combination of a transducing head and a writing location used for writing the data pattern on the magnetic medium is determined by the assembly. A predetermined write delay value based on the combination and the data pattern is computed by the assembly which then writes the data pattern on the magnetic medium with reference to the write delay value so that when the data pattern is read back, the flux transitions are preceived to be at the same distance as when entered into the apparatus.

Abstract: An offset nulling system is provided for use in computer disk drives to identify and compensate for actuator head position offset errors attributable to dc offsets of the disk drive control circuitry, thereby obtaining improved head alignment wiht a designated track on a memory storage disk or the like. The system includes a microcontroller adapted during a calibration mode to identify the position offset error and direction for selected tracks located respectively at radially inner and radially outer regions of the disk, and to adjust head position incrementally relative to those tracks to subsantially eliminate position offset error. Thereafter, during a normal operation mode of the disk drive, the microcontroller functions at the conclusion of a track seek step to adjust the head through a position offset compensation value and direction derived by interpolation of the position offset compensation value and direction identified during the calibration mode, in accordance with the specific track address.